Numerous types of electrodialysis membranes have been described and many arrangements of such membranes in electrodialysis devices, such as stacks and the like are known. One of the main problems is due to the close proximity of membranes to each other and the necessity to form a tight seal between adjacent membranes and gaskets. Generally electrodialysis membranes are not suited for attachment by heat-sealing to polymeric or other gaskets. It is very hard to form a good bond between such membranes and spacers or gaskets, and as any leak causes damage to the process and equipment and this constitutes a serious problem. Due to the impossibility to obtain an integral unit of conventional ion exchange membranes with spacers or gaskets, quite complicated mechanical and other means are resorted to. In spite of this it is generally not possible to entirely eliminate leaks. Such devices are also complicated and expensive.